| At present,there is less and less land that can be developed at low cost in urban centers,which leads to problems such as difficult transportation of fill,narrow working face and difficult compaction,and poor compaction effect in earthwork backfill projects.At the same time,the increase in the production of construction solid waste has made the ecological environment problem increasingly serious.Under this background,this paper uses foaming agent and cement to modify the engineering waste soil mixed with recycled fine aggregate,a pumpable backfill soil mixed with construction solid waste(referred to as pumpable soil in this paper)was developed.Pumpable soil is made by using recycled fine aggregate and engineering waste soil as raw material soil,and then fully mixing cement,foam and water.It has the characteristics of pumpability and low compressibility.In this paper,the change law of mechanical and construction performance of pumpable soil is studied by changing the content of different composition materials.The main research contents and achievements of this paper are as follows:(1)Discussing the preliminary development process of pumpable soil from the aspects of raw material selection and experimental design,among them,when the foaming agent is selected,the foam performance of different types of foaming agents is measured by experiments.,finally,according to the comparison of foaming power,foam stability and price,it is concluded that LG-2258 foaming agent is a foaming agent for pumpable soil.(2)By studying the pore wall and pore volume of pumpable soil,analysis of the micromorphology and pore distribution of pumpable soil under different material dosages,exploring its curing mechanism with strength and low compressibility from a microscopic perspective The degree of hydration and cementation of different proportions in pumpable soil and the main source of strength are obtained by scanning electron microscope test;the main distribution interval of pumpable soil pore size and the variation law of pore size with the dosage are obtained by mercury intrusion method.(3)By studying the strength and compression characteristics of pumpable soil,while discussing the changing laws of the mechanical properties of pumpable soils,the control indexes for backfilling are analyzed.The influence of material content on the unconfined compressive strength and compression curve of pumpable soil is analyzed from the test results,the relationship between its strength and compressive modulus is obtained by fitting,using the relational expression and according to the backfill compression index,the backfill strength index of pumpable soil is obtained.Finally,the backfill control index of pumpable soil is:the compressive modulus is greater than 4 MPa,and the unconfined compressive strength is greater than 136 kPa,which provides a theoretical basis for the backfill application of pumpable soil.(4)Through the research on the construction performance of pumpable soil,analysis of the basic performance change law of the mixture under different proportions in the construction stage,in this way,the proportion parameters of the pumpable soil fluidity,stability and pumpability to meet the construction requirements are discussed,and the relationship between the density of pumpable soil and mobility,bleeding rate and pressure bleeding rate is clarified by data fitting,it provides a reference for the engineering application of selecting pumpable soils of different densities according to construction performance.(5)Comparing the comprehensive unit price of pumpable soil and other materials for foundation pit backfilling project,and analyzing its economic advantages.The results show that pumpable soil is superior to manual backfill soil in terms of transportation cost and labor cost,and superior to concrete in terms of material cost.Finally,it is suggested that when the manual backfill soil compaction is difficult or the transportation is inconvenient in the project,the pumpable soil should be preferred. |
PDF Full Text Request